Phased Array Antenna

ABSTRACT

A phased array antenna for a telecommunications satellite, that is deployable from a retracted condition to a deployed condition when the satellite is on-station, comprising a base member ( 12 ) of hexagonal form, and a plurality of deployable antenna panels ( 14 ) stacked one on top of the other on the base member ( 12 ) in the retracted condition, each antenna panel ( 14.1 - 14.6 ) being connected to a respective side edge region of the base by means of a respective back flap hinge ( 16.1 - 16.6 ), and the hinges having pivot points ( 18 ) that are offset relative to one another, such that the antenna panels ( 14 ) can be hinged sequentially one after the other from the stick to a position in which each panel is adjacent a respective base side edge region to provide an extended flat two-dimensional area when deployed.

This invention relates to a phased array antenna, particularly thoughnot exclusively, for use with telecommunications satellites.

BACKGROUND ART

Antenna structures onboard telecommunication satellites commonly includerigid reflectors, up to around 2.5 metres diameter, or more complexstructures, for example unfurlable wire mesh reflectors up to 9 metresacross. The array may operate as a transmit only, a receive only, or asa combined transmit/receive antenna.

Phased array antennas are in general use as compact, stationarystructures for the flexible direction of electromagnetic energy formulti-beam, fast reaction tracking radar and telecommunicationsantennas. They are mechanically static but which can be electronicallyreconfigured to transmit or receive signals over a defined coverageregion. For example ground based satellite terminals use phased arraysfor tracking and communicating with satellites in low earth orbit, andflat plate phased array antennas are used for reception of satellitedirect to home TV broadcasts.

Phased array antennas are used as an alternative to conventionalreflector antennas onboard communications spacecraft. Examples includethe Boeing Gapfiller military satellite, which uses fixed(non-deployable) separate receive and transmit X-band arrays(http://www.boeing.com/defense-space/space/bss/factsheets/702/wgs/wgsfactsheet.html) and the Boeing Spaceway commercial satellite system,which uses which uses fixed Ka band phased arrays(http://www.boeing.com/ids/allsystemsgo/issues/vol1/num3/story06.html).These antennas are of relatively small aperture and are fixedstructures.

SUMMARY OF THE INVENTION

In at least a preferred embodiment, a deployable planar phased arrayantenna system for a telecommunications satellite is of a large aperturedesign and is deployed after the satellite is on-station in space. Thelarger aperture facilitates the generation of smaller diameter spotbeams on the earth's surface, enabling system capacity to be increasedthrough higher orders of frequency re-use. The smaller beam size alsocorresponds with an increase in the satellite transmitter EIRP(Effective Isotropic Radiated Power) and receiver sensitivity permittingoperation with small, low power, lower cost terminals.

The present invention provides in a first aspect a phased array antenna,deployable from a retracted condition to a deployed condition,comprising a base member having, at least in part, a polygonalcross-sectional form defined by a plurality of edge regions, and aplurality of antenna panels, each antenna panel being connected, by arespective hinge means, to a respective one of said edge regions of saidbase member, such that, in said retracted condition, two or more of theantenna panels are stacked one on top of the other on the base member,and the hinge means being such that the antenna panels can be hingedsequentially one after the other from the stack to a position in whicheach panel is adjacent a respective base edge region to provide saiddeployed condition wherein the phased array antenna provides an extendedarea.

The top surface of the base member preferably provides a further antennapanel. In order for the antenna to function correctly, the panels andbase member may preferably present a flat two dimensional surface,otherwise undesirable phase increments may arise between radiatorelements. The upper surfaces of the panels may be aligned with the uppersurface of the base member in the deployed condition; minor steps ordiscontinuities may however be corrected by signal processing.

The polygonal cross-sectional shape may be of any shape, but ispreferably regular. It may be triangular, rectangular, pentagonal, etc,but in one preferred form, from electrical considerations of antennadesign, is hexagonal, with six sides. The antenna panels may have thesame cross-section as the base member, and are stacked on top of thebase member so as to present a uniform cross-section in a lengthwisedirection. This is particularly desirable where the antenna forms partof a telecommunications satellite that has to be launched through theearth's atmosphere. The panels may however have different cross-sectionsif necessary. In one preferred form, the outer edges of each panel havea castellated form, so that sub-arrays of radiator elements may have anoptimum configuration.

As preferred, the panels are shaped and dimensioned that in the deployedcondition, edges of the panel are coterminous with the respective baseedge region. This permits electrical continuity of the antenna, andpermits electrical connections to be made across the edges. Edges ofeach panel extending from the base edge region may be positioned next tothe corresponding edge of an adjacent panel; in this way, the area ofthe antenna as deployed is closed.

In an alternative construction, an additional set of antenna panels maybe provided, each additional antenna panel being hinged to one of theabove first mentioned antenna panels, so that when the antenna panelsare deployed from the retracted condition, firstly a first antenna panelis moved to the deployed position, and subsequently the additionalantenna panel is pivoted from a position lying on top of the first panelto a deployed position. In this way, an antenna with a very large areamay be provided.

In the deployed position, the antenna provides preferably, roughly acircular closed area, so that the antenna provides an optimally largeaperture.

In a preferred manner of hinging the first antenna panels, each antennapanel is coupled to the base member by means of a hinge means having apivot point that is positioned relative to the position of the antennapanel in the retracted stack of antenna elements, so that the antennapanel upon rotation of the hinge to the deployed condition, makes a 180°rotation and a translatory movement to the plane at the top of the basemember in the fully deployed position.

The hinge is preferably of a “back-flap” construction, with a supportframe extending from the pivot point over the underside of the panelmember; in this way, it does not interfere with the electricalcharacteristics of the antenna. The pivot of the hinge is preferablyformed as an elongate sleeve and pin arrangement, to ensure that thepivot point remains accurately positioned throughout.

The stack of antenna panels may comprise all of the panels to one sideof the base member. Alternatively one or more antenna panels may bedisposed when retracted on the opposite side of the base member. Thismay be the case where the antenna is intended for a telecommunicationssatellite, where the base member is coupled to a service module by meansof a boom member, in order to avoid collision with the boom member.

In a preferred configuration, the antenna is disposed on top of thesatellite service module during the launch phase, but when the satelliteis on-station, then the antenna is rotated through 90°, in its retractedcondition, by means of the boom member, to a position where the antennais deployed. In this condition, the whole service module, including thedeployed solar arrays, is able to rotate relative to the antenna (onceevery 24 hrs). Such an arrangement is known and is for example describedin Communications Satellites, The Technology of Space Communications,Published 1987 by Heinemann, Author J. L. Blonstein, page 147. Theantenna points at the earth while the service module solar arrays pointat the sun. The solar arrays are fixed to the service module and do notrotate relative to the service module. In the preferred configuration,the base unit has to rotate 90° relative to the boom arm connecting itto the service module before the stowed panels can be deployed. The boomarm blocks the deployment of one panel from the rear of the base unit.The simplest arrangement is to have the “missing” panel fold directlyfrom the front face of the base unit. More panels could be stacked onthe front face of the base unit but the backflap hinge design means thatmechanical hinge parts (possibly electrically conductive) would projectin front of the antenna active surface, thereby disrupting the radiationpattern. It is the projection of mechanical parts in front of theantenna aperture that this invention avoids.

In a further aspect, the invention provides a telecommunicationssatellite comprising a service module and a phased array antenna coupledto the service module by means of a boom member, the service moduleincluding solar panels, and the phased array antenna being deployablefrom a retracted condition to a deployed condition, wherein in theretracted condition, the antenna is positioned on top of the servicemodule, and the boom member including rotatable means so that theantenna, when deployed, can be rotated relative to the service module,and the antenna comprising a plurality of antenna panels, such that, insaid retracted condition, two or more of the antenna panels are stackedone on top of the other, wherein for deployment, the antenna is firstlymoved by means of the boom member to a position away from the servicemodule, and then the antenna panels are moved to a deployed conditionwherein the phased array antenna provides an extended area.

For each antenna panel, the upper surface of the panel, together withthe top surface of the base member, provide an array of radiatorelements of the phased array antenna. The radiator elements may bearranged in subarrays having a certain geometric shape. The outer edgesof each panel have a castellated form, so that sub-arrays of radiatorelements may have an optimum hexagonal configuration. The sub arrays mayextend over the edges of the panels onto the base member and adjacentpanels as required.

The lower surface of each panel has appropriate electrical conductorsand components for coupling the radiator elements. Such conductor tracksare coupled to the base member, across adjoining edges, throughappropriately designed electrical contacts in the deployed condition.For example the adjacent edges of each panel member and the base membermay have protruding electrical contacts that are spring loaded, or ofcantilever design for example, so that they make contact with somespring force to maintain electrical contact. Alternatively they may makea snap fit connection. However, in practice, simple proximity(capacitive) connections may be sufficient at Ka band frequencies. Theadvantage with the hinge construction of the present invention is thatit confers great mechanical rigidity to the positioning of the deployedpanel relative to the base unit. This facilitates a number of multi-pinconnector schemes because of the precision with which the male andfemale parts can be aligned.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described withreference to the accompanying drawings wherein:—

FIGS. 1A, 1B and 1C are perspective views of a first embodiment of theinvention comprising a spacecraft with a deployable antenna in aretracted condition, and with solar panels in furled and unfurledconditions;

FIGS. 2A to 2F are perspective views showing sequential steps in thedeployment of the antenna;

FIGS. 3A to 3C are perspective views of a second embodiment of theinvention with FIG. 3A showing the antenna of the telecommunicationssatellite in a retracted position, FIG. 3B showing the antenna in araised position from the body of the satellite, and FIG. 3C showing thefully deployed antenna array;

FIG. 4 is a plan view of the deployed array showing the antenna panelsforming a roughly circular closed surface;

FIG. 5 shows constructional details of each antenna element; and

FIG. 6 shows, in schematic form, a cross-sectional view of a centralbase unit with antenna panels connected to the central unit by hinges.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the preferred embodiments of the invention, a phased array antennacomprises a number of antenna panels, which are hinged together andfolded when stowed prior to deployment. On deployment the array isunfolded to form a continuous large planar antenna aperture. Eachantenna panel comprises a multiplicity of active antennas. Thecomposition of each of these active antennas depends on the functioningof the array, transmit/receive, receive only, transmit only.

Referring now to FIGS. 1 and 2, a first embodiment comprises atelecommunications satellite having a service module body 2 and adeployable antenna 4 that is positioned in a retracted condition coaxialwith the body 2.

Both the body and the antenna are of hexagonal cross section. Theantenna is mounted to the body by means of a boom 6. Boom 6 is coupledto antenna 4 through a swivel joint 8 that permits rotation in twoplanes, as will become apparent. Stay members 10 are provided forholding the antenna in the position shown. The service module body 2 hassolar panels 11.

The antenna comprises a base member 12 and a stack of individual antennapanels 14, one antenna panel 14.1 being mounted on top of the base 12and the remaining five antenna panels 14.2 to 14.6 being mounted beneaththe base 12. The cross sectional shape of base 12 is defined by sides oredge regions 12.1 to 12.6. Each panel is mounted to a respective side ofbase 12 by a respective hinge 16.1 to 16.6. Each hinge has a pivot 18secured to a side of the base and comprising an extended sleevecontaining a rotatable pin (not shown). A frame 20 extends from therotatable pin to the respective panel 14. The frame is angled with aquadrilateral section as shown, and a further quadrilateral section maybe secured to the rear side of the antenna panel (not shown).

As shown in FIG. 1, in initial steps, before antenna deployment, solarpanels 11 are firstly unfurled, as shown in FIG. 1B, to a fully extendedposition, and then stay members 10 fall away, as shown in FIG. 1C.

As shown in FIG. 2, the method of deploying the antenna is firstly tomove the retracted antenna stack 4 to a position raised from the body 2and rotated through 90°, by means of swivel joint 8 attached to boom 6(see FIG. 1A, FIG. 1B and FIG. 2A).

As shown in FIG. 2B, a first antenna panel 14.1 that is initiallypositioned on top of body member 4, is hinged, by means of a hinge 16.1(FIG. 1C) mounted to base edge region 12.1, to the position as shownwherein the panel 14.1 extends coplanar with the top 24 of the base andwith the respective edges 12.1, 26 of the base and panel being locatedclose together and coterminii with one another. In this position,electrical contacts 27, formed as proximity capacitive contacts, aredisposed along the edges 12.1, 26 are electrically coupled. It will benoted that panel 14.1 is mounted on top of base member 4, sinceotherwise boom member 6 would be positioned across the active surface ofthe antenna panel, and degrade the antenna characteristics.

Then, as shown in FIGS. 2C to 2G, the antenna panels from the stackbehind the base are sequentially hinged to positions coplanar with panel14.1 and located against sequential edges of the base member 12. Theside edges 28 of each panel extending from the base are locatedcoterminii with adjacent edges 28 of adjacent panels. The result is, inthe fully deployed condition shown in FIG. 2G, a pattern of hexagons,seven in number including base top 24, that form a closed surface areathat is very roughly circular in outline and which provides an optimumconfiguration for a phased array antenna for telecommunications. Eachupper surface of the antenna panels and the upper surface of the basecarry arrays of radiator elements of the phased array antenna.

In the fully deployed condition, the swivel joint 8 permits the antennaand the service module to rotate relative to one another so that thesolar cells are directed at the sun, whereas the antenna remainsdirected at the earth. Such an arrangement is known and is for exampledescribed in Communications Satellites, The Technology of SpaceCommunications, Published 1987 by Heinemann, Author J. L. Blonstein,page 147. The only rotation is between antenna and service module, withelectrical power travelling along the boom arm that joins these twostructures. Only one simple electrical rotating joint is required (+−DC,50V, for example), compared with the dual complex rotational electricalconnections between a pair of solar panels and a conventional satellitebody. In the preferred configuration, the base unit has to rotate 90°relative to the arm connecting it to the service module before thestowed panels can be deployed. The arm blocks the deployment of onepanel from the rear of the base unit. The simplest arrangement is tohave the “missing” panel fold directly from the front face of the baseunit.

Details of the hinge arrangements for the antenna panels areschematically shown in FIG. 6, wherein two antenna panels 14.5, 14.6 ofthe stack are connected by respective back flap hinge members 16.5, 16.6to respective sides 12.5 and 12.6 of base unit 12. The pivot point ofthe hinge along the side of base unit 12 is different for each element,and for hinge 16.5 the pivot point is shown as at 60 and for hinge 16.6the pivot point is shown as at 62. The precise position of the pivotpoint is dependent on the position of the panel in the stack so thatwhen the hinging operation takes place, the panel hinges from the stackto a position adjacent the top edge of the base unit. Thus, each panelhinge has a unique offset dimension, being incremented relative to ahinge for an adjacent panel in the stack by half the thickness of thepanel. Referring to FIG. 6, A−B=0.5 panel effective stowed thickness.The hinge construction ensures no hinge line in front of the aperturethat would otherwise interfere with RF radiation. When the panels are intheir deployed condition, electrical connectors along the coterminiiedges of the panels and base member provide electrical coupling for theradiator elements (not shown). Simple robust hinge style offers preciseedge alignment and inter-panel electrical interconnects, as describedabove.

Referring now to the second embodiment shown in FIGS. 3, 4 and 5, atelecommunications satellite comprises a service module body member 42with an antenna 44 mounted coaxial with the body member 42 in aretracted condition, see FIG. 3A. A boom member 46 couples the antennato the body member. The antenna comprises a base member 48, a stack ofindividual antenna panels 50 mounted on one side of base member 48, anda single antenna panel 50.1 mounted on the opposite side of the basemember. As shown in FIG. 3B the first step in deploying the antenna isto move the antenna 44 by means of the boom 46 to a position rotated at90° to body member 42. The antenna panels 50.1 to 50.6 are thensequentially hinged from the stack along the respective edges of thebase member 48, so as to provide the configuration shown in FIG. 3C, ina similar manner to that described above with reference to FIG. 2. Inparticular, each panel 50 extends coplanar with the top of the base andwith the respective edges 54, 56 of the base and panel are located closetogether and coterminii with one another. The side edges 58 of eachpanel extending from the base are located coterminii with adjacent edges58 of adjacent panels. The configuration is more specifically shown inFIG. 4.

It will be noted that the antenna panels of the second embodiment arenot regular hexagons but that their outer edges 60 have castellations62. This permits as shown in FIG. 4 the phased array of radiatingelements 64 to be arranged in hexagonal sub-arrays 66. Each sub-array 66comprises nineteen radiating elements 64 arranged in a hexagonalconfiguration. The sub-arrays for each antenna panel occupy the outercastellations 62, and extend over into the adjacent edge regions 54 ofthe central base member 48 so as to preserve a regular hexagonalconfiguration. It may be seen that the central base member 48 also has asimilar array of hexagonal sub-arrays 66. In the result an array ofseven panels are provided each panel having a configuration of hexagonalsub-arrays, the sub-arrays all being of the same shape and size. Theresult is a phased array antenna of optimum configuration, having anapproximately circular shape for large aperture, with the hexagonalarrays of radiator elements providing optimum beam formingcharacteristics.

When the panels are in their deployed condition, electrical connectors(not shown) along the coterminii edges of the panels and base memberprovide electrical coupling for the radiator elements. Simple robusthinge style offers precise edge alignment and inter-panel electricalinterconnects.

Details of the construction of the radiating elements are shown in FIG.5 wherein electronic circuits 72 are connected to each radiating element60 through electrical conductors 74 extending perpendicular to thesurface of the antenna panels. For a Transmit/Receive array, each subarray 66 comprises a set of 19 radiating elements, a power divider whichenables these elements to be excited by a single source with definedpower division ratios and relative phases, a low noise amplifier (LNA)78 for low noise signal reception, a high power amplifier (HPA) 80 forsignal transmission, a bandpass filter 82 for rejecting unwanted, out ofband transmissions from the HPA, and a diplexer 84 for combining thereception and transmission paths into a common path for connection tothe set of radiating elements, and a beam-forming network. For atransmit only array the LNA and diplexer are omitted. For a Receive onlyarray, the HPA and bandpass filter are omitted, and the diplexer isreplaced by a bandpass filter.

An antenna panel is a combination of a modular design (for the assemblyof LNA, HPA, diplexer and filters) and single structural elements (forthe antenna front face carrying the radiating elements, thebeam-formers, heat pipes and supporting structures). This arrangementresults in reduced cost (for the modular assemblies), and reduced massoverall through the use of single structural elements.

The phased array antenna of the invention, as described, provides thefollowing advantages:

-   -   A large antenna aperture enables generation of small spot beams        permitting a high order of frequency re-use and enhancement of        system capacity. The small beams also enhance the transmitter        EIRP, and receive sensitivity enabling operation with small, low        power, low cost terminals.    -   A single phased array can replace a number of conventional        reflector antennas. This feature provides the following        benefits:        -   Lower total antenna mass. This translates into lower            spacecraft launch mass with attendant cost savings.            Alternatively the antenna mass saving could be used for            incorporating additional utility.        -   More compact structure, and takes up less room than the            reflector equivalents. Again this opens up the possibility            of incorporating additional utility.        -   Replacement of multiple reflector antennas by a single            phased array simplifies deployment.        -   Easier accommodation within the spacecraft launch vehicle.        -   Potential cost reductions (only one phased array antenna to            replace a number of reflector equivalents).    -   A high degree of operational flexibility.        -   The coverage provided by the phased array antenna can be            reconfigured to match changing traffic distributions or new            mission requirements.        -   The array provides a method of adjusting the coverage to            compensate for orbit inclination, thereby increasing the            useful lifetime of the satellite and to compensate for            satellite pointing errors.    -   A method of designing antennas such that only small changes to a        generic design are required to customise the antenna for        different missions.    -   Ability to compensate for antenna distortions, both during        assembly, integration and test on the ground, and during        operation in orbit.    -   Less susceptibility to scatter effects, and shadowing by        spacecraft structures than for reflector equivalents.    -   The planar array can be a self-contained unit with active        electronic units (HPAs and LNAs etc.) and filters integrated        into the assembly. This enables the assembly, integration and        test of the whole payload to be carried out more efficiently.    -   The antenna aperture can be used as a thermal radiator.

Having thus described the present invention by reference to preferredembodiments, it is to be appreciated that the embodiments are in allrespects exemplary and that modifications and variations are possiblewithout departure from the spirit and scope of the invention. Forexample, different shapes/sizes and/or a different number of antennapanels could be used in the invention so as to realise the technicaleffect of the invention. Furthermore, as well as applications onboardtelecommunications satellites, the deployable phased array antenna ofthe invention could also be used for terrestrial communication systemsin which a large phased array aperture is required but which must betransportable or easy to relocate.

1. A phased array antenna, deployable from a retracted condition to adeployed condition, comprising a base member having, at least in part, apolygonal cross-sectional form defined by a plurality of edge regions,and a plurality of antenna panels, each antenna panel being connected,by a respective hinge means, to a respective one of said edge regions ofsaid base member, such that, in said retracted condition, two or more ofthe antenna panels are stacked one on top of the other on the basemember, and the hinge means being such that the antenna panels can behinged sequentially one after the other from the stack to a position inwhich each panel is adjacent a respective base edge region to providesaid deployed condition wherein the phased array antenna provides anextended area.
 2. An antenna according to claim 1, wherein each antennapanel is generally the same cross-sectional shape as said base member.3. An antenna according to claim 2, wherein each antenna panel ishexagonal in shape.
 4. An antenna according to claim 2, wherein outeredges of each antenna panel, when deployed, are castellated in form. 5.An antenna according to claim 1, wherein at least one antenna panel ismounted on the opposite side of the base member to said stack in theretracted condition.
 6. An antenna according to claim 1, wherein theantenna panels are arranged such that when they are moved from the stackto the fully deployed position an edge of the panel is located adjacentto and coterminii with a respective edge of the base member.
 7. Anantenna according to claim 1, wherein side edges of each deployed panelextending from the base member are adjacent respective side edges ofadjacent panels.
 8. An antenna according to claim 1, wherein eachantenna panel is coupled to the base member by means of a back flaphinge, having a pivot comprising an extended sleeve and rotatable pintherein, and a frame extending from said pin and secured to the rearside of the antenna panel.
 9. An antenna according to claim 1, whereineach antenna panel is coupled to the base member by means of a hingewherein the mounting point of the hinge is such in relation to theposition of the panel within the stack in the retracted condition thatwhen the hinge is rotated about the pivot point the respective panelfrom the deployed condition is coplanar with the other antenna panels.10. An antenna according to claim 9, wherein the mounting point of thehinge is incremented for sequential panels in the stack, by half thethickness of the antenna panel in the stack.
 11. An antenna according toclaim 1, including electrical connector means disposed along adjacentedges, in the deployed condition, of each panel and said base member, inorder to make electrical connection between the base member and elementsof the antenna within each panel.
 12. An antenna according to claim 1,wherein radiating elements of the phased array are arranged in regularlyconfigured sub-arrays, preferably hexagonal.
 13. An antenna according toclaim 12 wherein the outer edges of each panel in the deployed conditionare castellated, and the sub-arrays extend into the castellations, withsub-arrays adjacent the base member extending over the edges of the basemember.
 14. An antenna according to claim 1, wherein the upper surfaceof the base member provides a central antenna panel.
 15. A phased arrayantenna according to claim 1, incorporated in a telecommunicationssatellite, the satellite having a service module including solar cellpanels, and the antenna being coupled via a rotatable joint to a boommember that is mounted to the service module, to permit relativerotation of the antenna and service module in the deployed condition.16. A phased array antenna according to claim 15, wherein at least oneantenna panel is mounted on the opposite side of the base member to saidstack in the retracted condition, to permit deployment in front of saidboom member.
 17. A telecommunications satellite comprising a servicemodule and a phased array antenna coupled to the service module by meansof a boom member, the service module including solar panels, and thephased array antenna being deployable from a retracted condition to adeployed condition, wherein in the retracted condition, the antenna ispositioned on top of the service module, and the boom member includingrotatable means so that the antenna, when deployed, can be rotatedrelative to the service module, and the antenna comprising a pluralityof antenna panels, such that, in said retracted condition, two or moreof the antenna panels are stacked one on top of the other, wherein fordeployment, the antenna is firstly moved by means of the boom member toa position away from the service module, and then the antenna panels aremoved to a deployed condition wherein the phased array antenna providesan extended area.
 18. A satellite according to claim 17, wherein saidantenna includes a base member to which said boom member is mounted,said stack being mounted on one side of said base member, and in whichat least one antenna panel is mounted on the opposite side of the basemember to said stack in the retracted condition, to permit deployment infront of said boom member. 19-20. (canceled)